With regard to the question whether an opposition is inadmissible if the opponent is a "straw man" acting for some other person, the Enlarged Board of Appeal clarified in G 3/97 and G 4/97 (OJ 1999, 245 and 270) that the opponent is the person who fulfils the requirements of Art. 99(1) in conjunction with Art. 100 EPC, R. 55 and 56(1) EPC 1973 (R. 76 and 77(1) EPC). Filing the opposition renders this person formally the legitimate opponent. The fact that the opponent is acting on behalf of a third party does not render the opposition inadmissible. It is however inadmissible if the opponent's involvement is to be regarded as circumventing the law by abuse of due process. Such circumvention of the law arises, in particular, if:

- the opponent is acting on behalf of the patent proprietor. According to G 9/93 (OJ 1994, 891), a proprietor cannot oppose his own patent; opposition is an inter partes procedure, so the patentee and opponent must be different persons.

- if the opponent is acting on behalf of a client in the context of activities which, taken as a whole, are typically associated with professional representatives, without possessing the necessary qualifications (Art. 134 EPC 1973). This would be the case if a person not entitled to act as a professional representative were acting on a client's behalf and carrying out all the activities typically carried out by professional representatives, while himself assuming the role of a party in order to circumvent the prohibition on his acting as a professional representative.

However, circumvention of the law by abuse of process does not arise merely because a professional representative files an opposition in his own name on behalf of a client. In any case, the principle of the free evaluation of evidence applies. The burden of proof lies with the person alleging that the opposition is inadmissible. The deciding body has to be satisfied, on the basis of clear and convincing evidence, that such abuse is occurring.

Previously relevant case law (see T 10/82, OJ 1983, 407; T 635/88, OJ 1993, 608; T 25/85, OJ 1996, 81; T 582/90, T 289/91, OJ 1994, 649; T 548/91, T 339/93, T 590/93, OJ 1995, 337; T 798/93, OJ 1997, 363) has been superseded by G 3/97 and G 4/97.

In T 2365/11 the notice of opposition was filed by a natural person; however, in a submission (to indicate the language which would be used during the oral proceedings) the opponent's attorney had referred to a certain company as the opponent. The patentee took the view that the law had been circumvented by abuse of due process. The board held that the opponent was clearly identified in the notice of opposition. Whether or not the correctly identified opponent was acting on behalf of a third person did not affect the admissibility of the opposition. The situations described in G 3/97 (order 1(b) and (c)) as circumvention of the law by abuse of process could be excluded in the present case.

Parallel cases T 1553/06 and T 2/09, involving the same parties but different patents, were heard by the same board. Considering the admissibility of the respective oppositions, the board examined in particular whether the parties and their representatives had worked together on a test case in order to obtain answers from the EPO to specific legal questions regarding prior art. Following the principles set out in G 9/93 and G 3/97, the board emphasised the contentious nature of opposition proceedings as a necessary condition for the admissibility of the opposition and examined whether an abuse of procedure, i.e. because the opponent acted on behalf of the patent proprietor ("straw man"), rendered the opposition inadmissible. The board could not find a circumvention of the law by abuse of process as it saw no reason to doubt the parties' submissions that the opponent was not bound by any instructions from the patentee or the study committee. An opposition filed within the framework of a test case was not inadmissible for that sole reason, provided that the prosecution of the proceedings thereby instituted was contentious because the parties defended mainly opposing positions. The respective oppositions were therefore deemed admissible.